Nuclear magnetic resonance (NMR) techniques are gaining increasing acceptance in clinical practice and medical research. With the development of NMR scanners, it is now possible to obtain structural and functional information of tissues in a living organism by non-invasive means. The NMR parameters such as the spin-lattice relaxation times (T1), spin-spin relaxation times (T2), and chemical shifts of tissues are altered by pathophysiologic events. Spatial localization of these changes in the NMR parameters provides the structural information in form of images, and measurement of the magnitude of change gives an insight into the functional state of tissue. The NMR techniques will be used to study the in vivo and in vitro pathophysiologic changes in the skeletal muscles of a well-characterized animal model. Experiments will be designed to test the hypothesis that normal and pathophysiologic events alter the physical properties of cellular water as measured by the NMR parameters. Initial studies will examine the relationship of T1 and T2 with the intrinsic metabolic (oxidative or glycolytic) characteristics of several predominantly fast and slow muscles. The changes in the NMR characteristics of these muscles during ontogenic development will be determined. Hypertrophy and atrophy will be induced in the muscles by genetic and experimental manipulations and their specific effects on the NMR parameters will be investigated. Different techniques of measurements will be used to distinguish structural and functional abnormalities in muscles due to compensatory physiologic responses and pathologic interventions. The role of hydration in changing the NMR relaxation times will be studied by controlled in vivo dehydration of muscles. Pharmacologic intervention will be used to examine to what extent changes in protein content and composition influence the NMR relaxation times of muscles. The contribution of protons from fat and water to the NMR parameters of muscles will be determined in lines selected for high or low fat. Finally, we will examine the relationship between in vitro and in vivo NMR measurement of muscles. The results from all these experiments will provide useful information for detection and monitoring the progression of muscle diseases.